1. Field of the Invention
The present invention relates to a system for controlling the temperature of a fluid additive for an exhaust system of an internal combustion engine, in particular of a urea-water solution for an SCR catalytic converter system in a motor vehicle.
2. Background
In motor vehicle technology, in diesel engines in particular, use is made in part of so-called SCR (selective catalytic reduction) catalytic converters, with an aqueous, for example 32.5% urea water solution being used as a NOx-reducing additive. Here, it is a known problem that a urea-water solution, on account of a relatively high freezing point (approximately −11° C.), tends to freeze even at ambient temperatures which are not uncommon depending on weather conditions and geographical location.
EP 1 698 769 A2 therefore describes a method and a device for supplying an additive for exhaust-gas purification in a vehicle, with the additive being heated to a temperature above its freezing point for the reasons stated above. This may take place either by means of the heat of the engine coolant or by means of the heat loss from a so-called retarder. However, both of these heat sources are available only after the vehicle has been operating for a certain period of time, such that no heat or an insufficient level of heat is available during a cold start phase.
DE 198 18 649 A1 describes a vehicle air conditioning system in a particular use with a heating mode (“heat pump mode”) for heating the engine coolant, and therefore in the case of a cold start, for heating up the engine and the passenger compartment more quickly.
The object on which the present invention is based is that of creating a system of the generic type described in the introduction, by means of which the temperature of a liquid additive can be controlled particularly effectively, even during an engine cold start phase.
According to the invention, this is achieved by means for exchanging heat between the additive of the exhaust system and a refrigerant circuit of a practically arbitrary “refrigeration system”, such as in particular an air conditioning system. It is therefore possible in particular for an SCR reducing additive to be directly or else indirectly heated, or cooled by means of a “switchover mode” if required. The exchange of heat can take place very quickly and with a very high level of efficiency even after a start-up of the engine and of the refrigeration system. A refrigeration system may possibly also include a vehicle cold room system in the mode as a “heat pump”.
Further advantageous design features and special embodiments of the invention are described in the dependent claims and in the following description.